The present invention relates to a dishwasher, and more particularly to a dishwasher which fits within the counter space typically available for a U.S. residential dishwasher and is operable on a U.S. residential power supply, yet meets the high sanitary requirements of a commercial dishwasher within a convenient cycle time.
Washing involves subjecting the surfaces of the dishes to sprays of a hot water and detergent solution for the purpose of removing food, grease, and other soiling material. Rinsing is the application of hot water to the surfaces of clean dishes.
Etching is a problem with glassware. Etching is the process through which a cloudy film develops on glasses over time. Etching is caused by a combination of several factors, including water hardness, soap, temperature and length of time at which the glassware is exposed to elevated temperatures. Given that soap and water hardness are relatively constant for a residential dishwasher, it is desirable to avoid holding glassware under high temperatures (above 150° F.) for extended periods of time (over 20 minutes). Preferably, dishwashers should not subject glassware to temperatures over roughly 150° F. (66° C.) for longer than roughly 20 minutes—or they will induce an unacceptable amount of etching. These standards are not specifically defined, however, since the exact conditions under which etching occurs are not precisely known and vary for different glassware products.
A commercial hot water sanitizing dishwasher must comply with the joint International Standard set by the NSF (National Sanitation Federation) and ANSI (American National Standard Institute)—namely, NSF/ANSI 3-2001. This commercial hot water sanitizing dishwashing machine standard is postulated in terms of three tests: First, the complete cycle shall render dishes free of soil and detergents. Second, the complete cycle shall deliver a minimum of 3,600 HUEs (heat unit equivalents at the surface of the dishes), with varying amounts of HUEs (as set forth in a chart) being added for each second that the surface of the dishes is at a temperature above 143° F. during the wash/rinse cycles. Third, for a hot water sanitizing machine having a stationary rack (as opposed to a conveyer) the machine shall provide either a single temperature of a 165° F. (74° C.) for both the minimum wash temperature and the minimizing rinse temperature or a dual temperature of 150° F. (66° C.) for the minimum wash temperature at 180° F. (82° C.) for the minimum sanitizing rinse temperature. In both instances the sanitizing rinse pressure should be at a pressure of 20 psi±5 psi±(138 kPa±34 kPa).
Accordingly, most commercial hot water sanitizing dishwashers today (e.g., a door-type Jackson TEMPSTAR dishwasher) use a fairly high volume (e.g., about eight gallons) of recirculating water under fairly high pressure (about 20 psi) at at least 150° F. to wash for roughly about 45–48 seconds (6.5 HUEs/sec.), then rinse with water at at least 180° F. for roughly about 11–12 seconds (346.8 HUEs/sec.). Such dishwashers have a complete cycle time of about one minute, generate about 4,107 HUEs, and are said to operate under the dual temperature (150° F./180° F. wash/rinse) implementation of the sanitization standard. However, other commercial hot water sanitizing dishwashers implement the sanitization standard by using 165° F. water for both the wash cycle and the rinse cycle. As all temperatures above 165° F. have a value of 346.8 HUEs, a combined wash/rinse period of 11 seconds at at least 165° F. generates about 3,814 HUEs. Such dishwashers are said to operate under the single temperature (165° F./165° F. wash/rinse) implementation of the sanitization standard.
Commercial dishwashers in the United States (and even residential dishwashers in many European countries) are capable of meeting such stringent requirements in minutes or less since they have available to them an ample 220/240 volt, 30–40 amp power supply. On the other hand, a residential dishwasher in the United States typically has available to it only the customary 110–120 volt, 15–20 amp household power supply. Accordingly, the conventional U.S. residential dishwashing systems cannot attain either the 150° F./180° F. or the 165° F./165° F. implementation of the sanitization standard for U.S. commercial dishwashers unless the dishwasher cycle extends for an inordinate amount of time, presumably at least about 90 minutes. The hot water available to a U.S. residential dishwasher is typically at 120° F.–140° F., 120° F. being the most common and 140° F. being the common practical maximum. Accordingly, unless there is a dedicated hot water heater external of the dishwasher to increase the temperature of the hot water supply available to the dishwasher, it is difficult, if not impossible, for the dishwasher—by virtue of its sump reheater alone—to raise the surface temperature of the dishes to above 143° F. and maintain them at that temperature (as necessary to accumulate HUEs) within an acceptable time for a residential dishwashing cycle. Thus, for the most part, U.S. residential dishwashers, even those taking an hour or so for the complete cleaning cycle, do not accumulate any HUEs, let alone enough to meet the sanitization standard.
Informal industry standards and experience for U.S. residential dishwashers dictate, first that there be at least four cycles—including a bathe cycle, at least one wash cycle, and at least one rinse cycle—to achieve effective cleaning of soiled kitchenware. Each cycle requires at least 1.5 gallons of water, typically 1.5–2.0 gallons, in order to obtain the desired cleaning. Second, the dishwasher must be able to operate with the limited U.S. residential power supply (110–120 volt, 15–20 amp power supply) and with the common maximum hot water supply available thereto (140° F.). Third, the dishwasher must operate within a convenient cycle time, and in any case a cycle time which does not involve subjecting glassware to temperatures over roughly 150° F. for longer than about twenty minutes in order to avoid etching of the glassware. Taken in combination, these three informal industry standards—four cycles, limited power, and limited time—pose rather difficult restrictions on the U.S. residential dishwasher, as each of the four cycles involves the introduction of at least 1.5 gallons of water at a maximum of 140° F., which water must be brought up to a higher temperature within a limited period of time using a limited power supply. Complicating the problem of bringing the water to appropriate sanitizing temperatures is the fact that each cycle of the U.S. residential dishwasher—whether bathe, wash, or rinse—begins with the introduction of water which is typically at a maximum of 140° F. The conventional heating element in the recirculating sump of the U.S. residential dishwasher has available to it only about 500–800 Watts of power (that is, the standard U.S. residential electrical power input minus the amount of power required to run the sump recirculating pump and controls). Thus, the sump heating element can typically provide an increase in temperature of the system (that is, the approximately 52 lb. of water, kitchenware to be washed, and dishwasher cavity surfaces) of less than 1° F. per minute.
The conventional heating element of a dishwasher (located in the recirculating sump) must raise the temperature of not only the 1.5–3.0 gallons of water present in a given cycle (equivalent to 12–24 lbs. of water), but also the kitchenware to be cleaned, including dishes, pots, pans, silverware and like kitchen utensils (about 20 lbs.), and the cavity/rack/spray-on system of the dishwashing cavity (about another 20 lbs.). The power supply must not only feed such heating element, but also perform the non-heating functions of the dishwasher—e.g., driving the pump that circulates the water under pressure into and around the cavity, driving the controls of the consumer interface, and the like. Thus it is not surprising that the time required to meet either implementation of the sanitization standard would be longer than an hour for a U.S. residential dishwasher.
Separate and apart from the constraint imposed on a U.S. residential dishwasher by the limited power supply available, there is also a constraint on the size or volume of a U.S. residential dishwasher. Both builder-supplied dishwashers (for new home construction) and replacement dishwashers are expected to fit within a given volume of “counter space,” which has become standardized over time at 35″×24″×23″ to provide a dishwasher cavity of about 7 cubic feet. The standard volume evolved in a way that allowed the dishwasher to fit under a counter at the standard kitchen counter height, with a door at a height at which consumers felt comfortable loading dishes, and a combined height and width that didn't take up too much “cupboard” space yet held a reasonable number of dishes. Taking into account the height of the lower tray rollers, the thickness of the door itself, and the space between the bottom of the lower tray and the bottom of the dishwasher cavity leaves approximately 9 inches between the floor and the bottom of the dishwashing cavity. Within this limited height must fit all the working parts of the dishwasher (e.g., inlet water connection, electrical power connection, inlet water valve, motor, valves, hoses, controls, etc.) external of the dishwashing cavity. Any advancement in dishwashers which does not fit within the existing industry standard for “cupboard space” will simply not be commercially viable. Fortunately, due to technological advances in plastics forming, motor controls and the like, the size of the working parts of dishwashers has shrunk over time since their introduction, and, as a result, some of the space under the dishwashing cavity and above the floor is now available for improvements in the residential dishwasher.
Accordingly, it is an object of the present invention to provide a sanitizing dishwasher which in one preferred embodiment operates on a conventional U.S. residential power supply.
A further object is to provide such a dishwasher which in one preferred embodiment occupies only the conventional U.S. residential dishwasher cupboard space.
Another object is to provide such a dishwasher which in one preferred embodiment substantially surpasses the joint NSF/ANSI standard for commercial hot water sanitizing dishwashers.
It is also an object of the present invention to provide a dishwasher which in one preferred embodiment has a cleaning cycle which is effective for sanitization purposes, yet shorter in length than the non-sanitizing cleaning cycle of the conventional U.S. residential dishwasher.
It is another object to provide such a dishwasher which in a preferred embodiment fits within the conventional U.S. residential dishwasher cupboard space and uses the conventional U.S. residential power supply, but achieves within a convenient cycle time the same standard of sanitization as is set for commercial hot water sanitizing dishwashers.
It is a further object to provide such a dishwasher which is simple and inexpensive to manufacture, use and maintain.